Semiconductor device having milti-height structure and method of manufacturing the same

ABSTRACT

A semiconductor device having semiconductor device having a multi-height structure is provided. The semiconductor device having a multi-height structure includes a semiconductor substrate. A first structure and a second structure are respectively disposed on the semiconductor substrate and connected to each other. The second structure includes a limiting layer disposed on the upper surface of the semiconductor substrate, a first polysilicon layer disposed conformally on the limiting layer and the semiconductor substrate, and a second polysilicon layer disposed conformally on the first polysilicon layer. A ridge of the second polysilicon layer is disposed near an edge of the second structure beside the first structure, vertically aligned with the limiting layer and defined as a limiting block. A bottom anti-reflection coating (BARC) layer of a low-viscosity material blanketly overlying a top surface of the second structure has an external surface substantially parallel to the top surface of the second structure.

BACKGROUND

A flash memory is an electronic non-volatile computer storage medium that can be electrically erased and reprogrammed. It is used in a wide variety of commercial and military electronic devices and equipment. For the purpose of storing information, the flash memory includes an addressable array of memory cells typically formed from floating gate transistors. Common types of flash memory cells include stacked gate memory cells and split gate flash memory cells. Split gate flash memory cells are semiconductor devices, typically formed as part of integrated circuits. Recently, split gate flash memory cells have received great attention due to the development of high memory capacities (relative to other types of flash memory cells). Split gate flash memory cells have several advantages over stacked gate memory cells, such as lower power consumption, higher injection efficiency, less susceptibility to short channel effects, and over erase immunity.

However, when a bottom anti-reflection coating (BARC) layer includes a low-viscosity material, the BARC layer has a thinner thickness near an edge of a functional area. An external surface of the BARC layer overlying various features shows a steep slope from a central portion to the edge of the functional area, so that the external surface cannot be parallel to the top surface of the underlying features along a horizontal dot-line. The uneven thickness of the BARC layer causes the overlying control gates near the edge of the functional area to slide down, resulting in worse critical dimension uniformity (CDU) within the functional area.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a schematic cross-sectional view of a semiconductor device having a multi-height structure in accordance with various embodiments.

FIGS. 2A to 2H are schematic cross-sectional views of intermediate stages showing a method of fabricating a semiconductor device having a multi-height structure in accordance with various embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact.

Terms used herein are only used to describe the specific embodiments, which are not used to limit the claims appended herewith. For example, unless limited otherwise, the term “one” or “the” of the single form may also represent the plural form. The terms such as “first” and “second” are used for describing various devices, areas and layers, etc., though such terms are only used for distinguishing one device, one area or one layer from another device, another area or another layer. Therefore, the first area can also be referred to as the second area without departing from the spirit of the claimed subject matter, and the others are deduced by analogy. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Embodiments of the present disclosure are directed to a semiconductor device having a multi-height structure including a semiconductor substrate, a first structure having a first height and a second structure having a second height greater than the first height, in which the second structure includes a limiting layer, a first polysilicon layer and a second polysilicon layer, a ridge of the second polysilicon layer is disposed near an edge of the second structure beside the first structure, is vertically aligned with the limiting layer and is defined as a limiting block, for acting as a retaining wall to hold or restrain more BARC layer on the second structure, thereby preventing the BARC layer flowing down from a top surface of the second structure.

In some embodiments, as shown in FIG. 1, it is a schematic cross-sectional view of a semiconductor device having a multi-height structure in accordance with various embodiments.

Briefly, in FIG. 1, a semiconductor device 100 may include a semiconductor substrate 101. A first structure 107 and a second structure 109 are respectively disposed on the semiconductor substrate 101 and connected to each other. A ridge 125 is disposed near an edge 121 d of the second structure 109 beside the first structure 107, is vertically aligned with a very underlying limiting layer 106 and is defined as a limiting block. A bottom anti-reflection coating (BARC) layer 135 blanketly covers the first structure 107, the second structure 109 and the limiting block 125. Control gates 141 a, 141 b, 141 c and 141 d are disposed on an external surface 137 of the BARC layer 135.

As shown in FIG. 1, in certain embodiments, the semiconductor substrate 101 may be defined into two functional areas including a first functional area 103 and a second functional area 105, in which the first functional area 103 may be defined as a logic cell area, and the second functional area 105 may be defined as a flash cell area, for examples. However, in other embodiments, the first functional area 103 and the second functional area 105 may be other functional areas rather than the aforementioned definitions. In those embodiments, depending actual requirements, the semiconductor substrate 101 may include structures such as shallow trench isolations (STIs; not shown in the figures) to define areas for active devices, sometimes referred as OD areas (not shown in the figures).

As shown in FIG. 1, in some embodiments, the first structure 107 may be disposed on the semiconductor substrate 101. In certain embodiments, the first structure 107 may include a low-gate polysilicon layer 123 disposed above the first functional area 103 of the semiconductor substrate 101. In these embodiments, the first structure 107 includes a low gate polysilicon layer, and the first structure 107 may have a first height H₁ from an upper surface 102 of the semiconductor substrate 101 to a top surface (not shown in the figures) of the low-gate polysilicon layer 123.

As shown in FIG. 1, in some embodiments, the second structure 109 may be disposed on the semiconductor substrate 101 and adjacent to the first structure 107. In certain embodiments, the second structure 109 may include a limiting layer 106 disposed on the upper surface 102 of the semiconductor substrate 101, a first polysilicon layer 111 disposed conformally on the limiting layer 106 and the semiconductor substrate 101, and a second polysilicon layer 121 disposed conformally on the first polysilicon layer 111.

In some embodiments, the upper surface 102 directly refers to a surface of the semiconductor substrate 101. In other embodiments, an additional layer such as a passivation layer (not shown in figures) may be optionally disposed on the surface of the semiconductor substrate 101, and the upper surface 102 refers to a surface of the additional layer.

In some embodiments, the limiting layer 106 is not limited to specific materials. However, in certain embodiments, the limiting layer 106 may have a material the same as a typical hard mask or a typical passivation layer being formed by nitride-based material such as silicon nitride, silicon oxynitride (SiON), titanium nitride (TiN) and other appropriate materials of the hard mask or the passivation layer.

In some examples, a dielectric layer 113 may be optionally disposed between the second polysilicon 121 and the first polysilicon layer 111. The second polysilicon layer 121 may have a first portion 121 a disposed on the first polysilicon layer 111.

In certain embodiments, the first polysilicon layer 111 includes a floating gate polysilicon layer, and the second polysilicon layer 121 includes a high-voltage polysilicon layer having a first portion 121 a and a second portion 121 b. In some examples, the first portion 121 a is disposed on the first polysilicon layer 111. In some embodiments, the second portion 121 b of the second polysilicon layer 121 may be optionally extended along the upper surface 102 of the semiconductor substrate 101 and connected to the low-gate polysilicon layer 123.

In those embodiments, the first polysilicon layer 111, the second polysilicon layer 121 and the low-gate polysilicon layer 123 may include a polysilicon material doped with common concentrations of various known impurities. In these embodiments, the second structure 109 may have a second height H₂ from the upper surface 102 of the semiconductor substrate 101 to a top surface 121 c of the second polysilicon layer 121, and the second height H₂ is greater than the first height H₁. For example, a difference between the second height H₂ and the first height H₁ (i.e. the second height H₂ minus the first height H₁) divided by the first height H₁, i.e. (H₂−H₁)/H₁, may be greater than 3% and is greater than 10% in certain examples.

In some examples, a ridge 125 of the second polysilicon layer 121 is disposed near an edge 121 d of the second structure 109 beside the first structure 107, is vertically aligned with the limiting layer 106 and is defined as a limiting block. In these embodiments, a height of the ridge 125 is freely adjusted by a height of the very underlying limiting layer 106 depending upon the actual design requirements and viscosity of the overlying BARC layer 135. For example, the limiting layer 106 has a third height H₃ from the upper surface 102 of the semiconductor substrate 101. In those examples, the first polysilicon layer 111 has a fourth height H₄ from the upper surface 102 of the semiconductor substrate 101, and the third height H₃ is substantially equal to or greater than one fifth of the fourth height H₄. In some examples, the third height H₃ is substantially equal to or greater than one fourth of the fourth height H₄. In certain examples, the third height H₃ is substantially equal to or greater than one third of the fourth height H₄.

As shown in FIG. 1, in some embodiments, a bottom anti-reflection coating (BARC) layer 135 may blanketly covers the first structure 107, the second structure 109 and the limiting block 125. In these embodiments, in which the BARC layer 135 in liquid state may include a low-viscosity material having a viscosity of no more than 5000 centipoise (cp), for example. It is noted that cp is an abbreviation of centipoise, 1 P=1 g·s⁻¹·cm⁻¹, viscosity unit: Pa·s=kg·m⁻¹ s⁻¹, therefore 1 Pa·s=10 P=1000 cP.

It is noted that, the limiting block 125 acts as a retaining wall to hold or restrain more of the BARC layer 135 on the top surface 121 c and near the edge 121 d of the second structure 109, for preventing the BARC layer 135 flowing down from the top surface 121 c of the second structure 109. It keeps an external surface 137 of the BARC layer 135 overlying the top surface 121 c of the second structure 109 to be substantially parallel to the top surface 121 c of the second structure 109 along a horizontal dot line 139. That is to say, the BARC layer 135 has a substantially uniform thickness T above the top surface 121 c as shown in FIG. 1. Accordingly, the limiting block 125 may properly adjust the slope of the external surface 137 of the BARC layer 135 on the top surface 121 c of the second structure 109. In certain examples, the limiting block 125 may decrease the slope of the external surface 137 of the BARC layer 135 approximately to zero on the top surface 121 c of the second structure 109.

In some certain embodiments, the difference between the second height H₂ and the first height H₁ (i.e. the second height H₂ minus the first height H₁) is greater than zero. In other embodiments, depending upon the difference between the second height H₂ and the first height H₁ (i.e. the second height H₂ minus the first height H₁) divided by the first height H₁, i.e. (H₂−H₁)/H₁, the height of the limiting block 125 is arbitrary by adjusting the third height H₃ of the underlying limiting layer 106 freely rather than limiting the height of the limiting block 125. For example, when the difference between the second height H₂ and the first height H₁ (i.e. the second height H₂ minus the first height H₁) divided by the first height H₁, i.e. (H₂−H₁)/H₁, is greater than 10% in certain examples, the limiting block 125 has a height greater than another limiting block 125 when the difference between the second height H₂ and the first height H₁ (i.e. the second height H₂ minus the first height H₁) divided by the first height H₁, i.e. (H₂−H₁)/H₁, is less than 5%. So that the limiting block 125 may hold or restrain much more of the BARC layer 135 on the top surface 121 c and near the edge 121 d of the second structure 109, for enhancing the prevention of the BARC layer 135 flowing down from the top surface 121 c of the second structure 109.

As shown in FIG. 1, in some embodiments, control gates 141 a, 141 b, 141 c and 141 d may be disposed on the external surface 137 of the BARC layer 135. Since the external surface 137 of the BARC layer 135 overlying the top surface 121 c of the second structure 109 is extended along the horizontal dot-line 139 substantially parallel to the top surface 121 c of the second structure 109, there is no or little differences in height of the control gates 141 a, 141 b, 141 c and 141 d. That is to say, the BARC layer 135 has a substantially uniform thickness T above the top surface 121 c.

Referring to FIG. 1, in other embodiments, other material layers maybe optionally disposed below the BARC layer 135 and above the first structure 107, the second structure 109 and the limiting block 125. In certain embodiments, an anti-reflection dielectric (ARD) layer 131 may be optionally disposed to blanketly cover the first structure 107, the second structure 109 and the limiting block 125. In certain embodiments, another passivation layer 133 may be optionally disposed to blanketly cover the ARD layer 131, in which the passivation layer 133 includes silicon oxynitride (SiON).

The semiconductor device 100 of FIG. 1 can be manufactured as follows. FIG. 2A to FIG. 2H are schematic cross-sectional views of intermediate stages showing a method of fabricating a semiconductor device 200 having a multi-height structure in accordance with various embodiments.

In some embodiments, as shown in FIG. 2A, the semiconductor device 200 may include a semiconductor substrate 201. The semiconductor substrate 201 may be a semiconductor material and may include structures including a graded layer or a buried oxide, for example. In some exemplary examples, the semiconductor substrate 201 includes bulk silicon that may be undoped or doped (e.g., p-type, n-type, or a combination thereof). Other materials that are suitable for semiconductor device formation may be used. Other materials, such as germanium, quartz, sapphire, and glass could alternatively be used for the semiconductor substrate 201. Alternatively, the semiconductor substrate 201 may be an active layer of a semiconductor-on-insulator (SOI) substrate or a multi-layered structure such as a silicon-germanium layer formed on a bulk silicon layer. In certain embodiments, the semiconductor substrate 201 may be defined into two areas, a first functional area 203 and a second functional area 205. In those embodiments, the first functional area 203 may be defined as a logic cell area, and the second functional area 205 may be defined as a flash cell area. In those embodiments, the semiconductor substrate 201 may include structures such as shallow trench isolations (STIs) (not shown in the figures) to define areas for active devices, sometimes referred as OD areas (not shown in the figures).

In some embodiments, as shown in FIG. 2B, a limiting layer 206 may be formed on an upper surface 202 of the semiconductor substrate 201. In some embodiments, the upper surface 202 directly refers to a surface of the semiconductor substrate 201. In other embodiments, an additional layer such as a passivation layer (not shown in figures) may be optionally disposed on the surface of the semiconductor substrate 201, and the upper surface 202 refers to a surface of the additional layer.

In some embodiments, the limiting layer 206 is not limited to specific materials. However, in certain embodiments, the limiting layer 206 may have a material the same as a typical hard mask or a typical passivation layer being formed by nitride-based material such as silicon nitride, silicon oxynitride (SiON), titanium nitride (TiN) and other appropriate materials of the hard mask or the passivation layer.

In some embodiments, as shown in FIG. 2C, the semiconductor device 200 may include a first polysilicon layer 211 211 formed conformally above the limiting layer 206 and the upper surface 202 of a semiconductor substrate 201 within the second functional area 205. In certain embodiments, the first polysilicon layer 211 includes a floating gate polysilicon layer, and the first polysilicon layer 211 has a first protrusion 211 a formed and vertically aligned with the underlying limiting layer 206.

In some embodiments, as shown in FIG. 2C, the limiting layer 206 has a third height H₃ from the upper surface 202 of the semiconductor substrate 201. In those examples, the first polysilicon layer 211 has a fourth height H₄ from the upper surface 202 of the semiconductor substrate 201, and the third height H₃ is substantially equal to or greater than one fifth of the fourth height H₄. In some embodiments, the first polysilicon layer 211 has a fourth height H₄ from the upper surface 202 of the semiconductor substrate 201, and the third height H₃ is substantially equal to or greater than one fifth of the fourth height H₄. In some examples, the third height H₃ is substantially equal to or greater than one fourth of the fourth height H₄. In certain examples, the third height H₃ is substantially equal to or greater than one third of the fourth height H₄.

In some embodiments, as shown in FIG. 2D, a dielectric layer 213 may be optionally and conformally formed on the first polysilicon layer 211, in which a second protrusion 213 a is formed and vertically aligned with the underlying first protrusion 211 a and the limiting layer 206.

In some embodiments, as shown in FIG. 2E, a second polysilicon layer 221 may be formed on the first polysilicon layer 211 and optionally on the dielectric layer 213, in which the second polysilicon layer 221 has a ridge 221 e is formed and vertically aligned with the underlying second protrusion 213 a, the first protrusion 211 a and the limiting layer 206, and the ridge 221 e acts as a limiting block 225. In addition, in certain embodiments, the second polysilicon layer 221 may have a first portion 221 a formed on the first polysilicon layer 211, a second portion 221 b optionally extending along the upper surface 202 of the semiconductor substrate 201.

In those embodiments, the first polysilicon layer 211, the second polysilicon layer 221 and the low-gate polysilicon layer 223 may include a polysilicon material doped with common concentrations of various known impurities, and the first polysilicon layer 211, the second polysilicon layer 221 and the low-gate polysilicon layer 223 may be made from polysilicon or other appropriate conducting materials, which may be formed by a typical process, such as chemical vapor deposition (CVD) process.

In some embodiments, as shown in FIG. 2F, a low-gate polysilicon layer 223 may be formed the upper surface 202 of the semiconductor substrate 201 within the first functional area 203 and connected to the second portion 221 b of the second polysilicon layer 221. In certain embodiments, the low-gate polysilicon layer 223 and the second portion 221 b of the second polysilicon layer 221 may be defined as a first structure 207, as shown in FIG. 2F. The first portion 221 a of the second polysilicon layer 221, the low-gate polysilicon layer 211 and optionally the dielectric layer 213 may be defined as a second structure 209.

In some embodiments, as shown in FIG. 2F, an ARD layer 231 may optionally blanketly cover the first structure 207, the ridge 221 e and the second structure 209. Then, a passivation layer 233, including silicon oxynitride (SiON), may optionally blanketly cover the ARD layer 231.

In some embodiments, as shown in FIG. 2G, a BARC layer 235 may blanketly cover the passivation layer 233. In some embodiments, the BARC layer 235 in liquid phase may include a low-viscosity material having a viscosity smaller than or equal to 5000 centipoise (cp), for example. The BARC layer 235 may be applied on the passivation layer 233 by a typical spin coating process. It is noted that cp is an abbreviation of centipoise, 1 P=1 g·s⁻¹·cm⁻¹, viscosity unit: Pa·s=kg·m⁻¹ s⁻¹, therefore 1 Pa·s=10 P=1000 cP.

It is noted that, the limiting block 225 formed from the ridge 221 e, acting as a retaining wall, may be used to hold or restrain more of the BARC layer 235 on the top surface 221 c and near the edge 221 d of the second structure 209, for preventing the BARC layer 235 flowing down from the top surface 221 c of the second structure 209. It keeps an external surface 237 of the BARC layer 235 overlying the top surface 221 c of the second structure 209 to be substantially parallel to the top surface 221 c of the second structure 209 along a horizontal dot line 239. That is to say, the limiting block 225 has a substantially uniform thickness T above the top surface 221 c and appropriately adjusts the slope of the external surface 237 of the BARC layer 235 on the top surface 221 c of the second structure 209. In certain examples, the limiting block 225 may decrease the slope of the external surface 237 of the BARC layer 235 approximately to zero on the top surface 221 c of the second structure 209.

Referring to FIG. 2H. FIG. 2H is a schematic cross-sectional view of a semiconductor device having a multi-height structure in accordance with other embodiments. In other embodiments, as shown in FIG. 2H, the second polysilicon layer 221 of the second structure 209 may have a first portion 221 a, in which the first portion 221 a may be disposed on the first polysilicon layer 211. In these embodiments, the limit block 225 may be disposed on the top surface 221 c of the second polysilicon layer 221 of the second structure 209 near an edge 221 d of the second structure 209 beside the first structure 207. The limit block 225 is like a retaining wall. The limit block 225 also may hold or restrain the BARC layer 235 on the top surface 221 c of the second structure 209, for keeping the external surface 237 of the BARC layer 235 overlying the top surface 221 c of the second structure 209 to be substantially parallel to the top surface 221 c of the second structure 209 along a horizontal dot line 239. Accordingly, the limit block 225 also may freely adjust the slope of the external surface 237 of the BARC layer 235 on the top surface 221 c of the second structure 209. In certain examples, the limit block 225 may decrease the slope of the external surface 237 of the BARC layer 235 on the top surface 221 c of the second structure 209.

In some embodiments, as shown in FIG. 2H, control gates 241 a, 241 b, 241 c and 241 d may be disposed on the external surface 237 of the BARC layer 235 at substantially the same horizontal level.

In some examples, as shown in FIG. 2H, the first structure 207 has a first height H₁ from an upper surface 202 of the semiconductor substrate 201 to a top surface (not shown in the figures) of the low-gate polysilicon layer 223, the second structure 209 has a second height H₂ from the upper surface 202 of the semiconductor substrate 201 to a top surface 221 c of the second polysilicon layer 221, the limiting layer 206 has a third height H₃ from the upper surface 202 of the semiconductor substrate 201, and the first polysilicon layer 211 has a fourth height H₄ from the upper surface 202 of the semiconductor substrate 201, all of which depends upon the actual design requirements and viscosity of the overlying BARC layer 235.

In some examples, the second height H₂ is greater than the first height H₁, a difference between the second height H₂ and the first height H₁ (i.e. the second height H₂ minus the first height H₁) divided by the first height H₁, i.e. (H₂−H₁)/H₁, is greater than 3%, and is greater than 10% in certain examples. In addition, when the difference between the second height H₂ and the first height H₁ (i.e. the second height H₂ minus the first height H₁) divided by the first height H₁, i.e. (H₂−H₁)/H₁, is greater than 10% in certain examples, the limiting block 225 has a height greater than another limiting block 225 when the difference between the second height H₂ and the first height H₁ (i.e. the second height H₂ minus the first height H₁) divided by the first height H₁, i.e. (H₂−H₁)/H₁, is less than 5%. So that the limiting block 225 may hold or restrain much more of the BARC layer 235 on the top surface 221 c and near the edge 221 d of the second structure 209, for enhancing the prevention of the BARC layer 235 flowing down from the top surface 221 c of the second structure 209.

In some examples, the height of the limiting block 225 is arbitrary by adjusting the third height H₃ of the very underlying limiting layer 206 freely rather than limiting the height of the limiting block 225. In some examples, the third height H₃ is substantially equal to or greater than one fifth of the fourth height H₄. In other examples, the third height H₃ is substantially equal to or greater than one fourth of the fourth height H₄. In certain examples, the third height H₃ is substantially equal to or greater than one third of the fourth height H₄.

In some embodiments of the semiconductor device 200 having the limiting layer 206, the standard derivation in height of all control gates 241 a, 241 b, 241 c and 241 d of such semiconductor device 200 may have a mean of less than 2.6 and a standard derivation of less than 0.26 when the semiconductor device 200 has the limiting block 225. In certain examples, the standard derivation in height of all control gates of the semiconductor device 200 may have a mean of less than 2.4 and a standard derivation of less than 0.20 when the semiconductor device 200 has the limiting block 225. In other certain examples, the standard derivation in height of all control gates of the semiconductor device 200 may have a mean of less than 2.2 and a standard derivation of less than 0.16 when the semiconductor device 200 has the limiting block 225. The semiconductor device 200 of FIG. 2H may have improved (i.e. larger) CD near the edge 221 d of the second functional area 205 (for example, the flash cell area).

In comparison with the typical semiconductor device without the limiting block, when a BARC layer includes a low-viscosity material, an external surface of the BARC layer overlying various features shows a steep slope from a central portion to the edge of a functional area, the BARC layer is unlikely held or restrained on the top surface of the underlying various features. Moreover, for example, the BARC layer overlying the top surface of the underlying various features within a functional area has a mean of more than 2.6 and a standard derivation of more than 0.26, and the critical dimension uniformity (CDU) of the semiconductor device within the functional area become worse, leading smaller CD at the edge of the underlying various features (for example, the flash cell area). However, the semiconductor device 200 having the limiting block 225 (e.g. FIG. 2H) may improve approximately 25% CDU in comparison with the semiconductor device within the functional area.

In accordance with some embodiments, the present disclosure discloses a semiconductor device having a multi-height structure. The semiconductor device may include a semiconductor substrate, a first structure, a second structure, a bottom anti-reflection coating (BARC) layer and control gates. The first structure may be disposed on the semiconductor substrate, in which the first structure has a first height from an upper surface of the semiconductor substrate. The second structure may be disposed on the semiconductor substrate and adjacent to the first structure, in which the second structure may have a second height more than the first height from the upper surface of the semiconductor substrate. The second structure includes a limiting layer disposed on the upper surface of the semiconductor substrate, a first polysilicon layer disposed conformally on the limiting layer and the semiconductor substrate, and a second polysilicon layer disposed conformally on the first polysilicon layer, in which the limiting layer has a third height from the upper surface of the semiconductor substrate, the first polysilicon layer has a fourth height from the upper surface of the semiconductor substrate, and the third height is substantially equal to or greater than one fifth of the fourth height. A ridge of the second polysilicon layer is disposed near an edge of the second structure beside the first structure, is vertically aligned with the limiting layer and is defined as a limiting block. The bottom anti-reflection coating (BARC) layer may cover the first structure, the second structure and the limiting block, in which the BARC layer may include a low-viscosity material, and the BARC layer overlying a top surface of the second structure may have an external surface substantially parallel to the top surface of the second structure. The control gates may be disposed on the external surface of the BARC layer.

In accordance with some embodiments, the present disclosure discloses a semiconductor device having a multi-height structure. The semiconductor device may include a first structure, a second structure, an anti-reflection dielectric (ARD) layer, a BARC layer and control gates. The first structure may be disposed on a semiconductor substrate, in which the first structure may have a first height from an upper surface of the semiconductor substrate. The second structure may be disposed on the semiconductor substrate and adjacent to the first structure, in which the second structure may have a second height more than the first height from the upper surface of the semiconductor substrate. The second structure includes a limiting layer disposed on the upper surface of the semiconductor substrate, a first polysilicon layer disposed conformally on the limiting layer and the semiconductor substrate, and a second polysilicon layer disposed conformally on the first polysilicon layer. The limiting layer has a third height from the upper surface of the semiconductor substrate, and the first polysilicon layer has a fourth height from the upper surface of the semiconductor substrate, and the third height is substantially equal to or greater than one fifth of the fourth height. A ridge of the second polysilicon layer is disposed near an edge of the second structure beside the first structure, is vertically aligned with the limiting layer and is defined as a limiting block. The ARD layer may cover the first structure, the second structure and the limiting block conformally. The BARC layer may cover the ARD layer, in which the BARC layer may include a low-viscosity material, and the BARC layer above a top surface of the second structure may have an external surface substantially parallel to the top surface of the second structure. The control gates may be disposed on the external surface of the BARC layer.

In accordance with some embodiments, the present disclosure discloses a semiconductor device having a multi-height structure. The semiconductor device may include a first structure, a second structure, an ARD layer, a passivation layer, a BARC layer and control gates. The first structure may be disposed on the semiconductor substrate, in which the first structure may have a first height from an upper surface of the semiconductor substrate. The second structure may be disposed on the semiconductor substrate and adjacent to the first structure, in which the second structure may have a second height more than the first height from the upper surface of the semiconductor substrate. The limiting layer has a third height from the upper surface of the semiconductor substrate, and the first polysilicon layer has a fourth height from the upper surface of the semiconductor substrate, and the third height is substantially equal to or greater than one fifth of the fourth height. A ridge of the second polysilicon layer is disposed near an edge of the second structure beside the first structure, is vertically aligned with the limiting layer and is defined as a limiting block. The ARD layer may cover the first structure, the second structure and the limiting block conformally. The passivation layer may cover the ARD layer, in which the passivation layer may include silicon oxynitride (SiON). The BARC layer may cover the passivation layer, in which the BARC layer may include a low-viscosity material, and the BARC layer above a top surface of the second structure may have an external surface substantially parallel to the top surface of the second structure. The control gates may be disposed on the external surface of the BARC layer.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A semiconductor device having a multi-height structure, the semiconductor device comprising: a semiconductor substrate; a first structure disposed on the semiconductor substrate, wherein the first structure has a first height from an upper surface of the semiconductor substrate; and a second structure disposed on the semiconductor substrate and adjacent to the first structure, wherein the second structure has a second height from the upper surface of the semiconductor substrate, and the second height is substantially greater than the first height, the second structure comprising: a limiting layer disposed on the upper surface of the semiconductor substrate, wherein the limiting layer has a third height from the upper surface of the semiconductor substrate; a first polysilicon layer disposed conformally on the limiting layer and the semiconductor substrate, wherein the first polysilicon layer has a fourth height from the upper surface of the semiconductor substrate, and the third height is substantially equal to or greater than one fifth of the fourth height; and a second polysilicon layer disposed conformally on the first polysilicon layer, wherein a ridge of the second polysilicon layer is disposed near an edge of the second structure beside the first structure, is vertically aligned with the limiting layer and is defined as a limiting block; a bottom anti-reflection coating (BARC) layer covering the first structure, the second structure and the limiting block conformally, wherein the BARC layer comprises a low-viscosity material, and a plurality of control gates disposed on an external surface of the BARC layer.
 2. The semiconductor device of claim 1, wherein the first structure includes a low gate polysilicon layer.
 3. The semiconductor device of claim 2, wherein the first polysilicon layer includes a floating gate polysilicon layer, the second polysilicon layer includes a high-voltage polysilicon layer having a first portion and a second portion, and the first portion is disposed on the floating gate polysilicon layer.
 4. The semiconductor device of claim 3, wherein the second portion is extended along the upper surface of the semiconductor substrate and connected to the low gate polysilicon layer.
 5. The semiconductor device of claim 4, wherein the first structure includes the low gate polysilicon layer and the second portion of the high-voltage polysilicon layer disposed on the semiconductor substrate.
 6. The semiconductor device of claim 1, wherein the third height is substantially equal to or greater than one fourth of the fourth height.
 7. A semiconductor device having a multi-height structure, the semiconductor device comprising: a first structure disposed on a semiconductor substrate, wherein the first structure has a first height from an upper surface of the semiconductor substrate; and a second structure disposed on the semiconductor substrate and adjacent to the first structure, wherein the second structure has a second height from the upper surface of the semiconductor substrate, and the second height is substantially greater than the first height, the second structure comprising: a limiting layer disposed on the upper surface of the semiconductor substrate, wherein the limiting layer has a third height from the upper surface of the semiconductor substrate; a first polysilicon layer disposed conformally on the limiting layer and the semiconductor substrate, wherein the first polysilicon layer has a fourth height from the upper surface of the semiconductor substrate, and the third height is substantially equal to or greater than one fifth of the fourth height; and a second polysilicon layer disposed conformally on the first polysilicon layer, wherein a ridge of the second polysilicon layer is defined as a limiting block vertically aligned with the limiting layer, and is disposed near an edge of the second structure beside the first structure; an anti-reflection dielectric (ARD) layer covering the first structure, the second structure and the limiting block conformally; a BARC layer covering the ARD layer, wherein the BARC layer comprises a low-viscosity material; and a plurality of control gates disposed on the external surface of the BARC layer.
 8. The semiconductor device of claim 7, wherein the first structure includes a low gate polysilicon layer.
 9. The semiconductor device having a multi-height structure of claim 8, wherein the first polysilicon layer includes a floating gate polysilicon layer, the second polysilicon layer includes a high-voltage polysilicon layer having a first portion and a second portion, and the first portion is disposed on the first polysilicon layer.
 10. The semiconductor device of claim 9, wherein the second portion is extended along the upper surface of the semiconductor substrate and connected to the low gate polysilicon layer.
 11. The semiconductor device of claim 10, wherein the first structure includes the low gate polysilicon layer and the second portion of the high-voltage polysilicon layer disposed on the semiconductor substrate.
 12. The semiconductor device of claim 7, wherein the third height is substantially equal to or greater than one fourth of the fourth height.
 13. The semiconductor device of claim 7, wherein a passivation layer is disposed between the ARD layer and the BARC layer.
 14. The semiconductor device of claim 13, wherein the passivation layer comprises silicon oxynitride (SiON).
 15. A semiconductor device having a multi-height structure, the semiconductor device comprising: a first structure disposed on a semiconductor substrate, wherein the first structure has a first height from an upper surface of the semiconductor substrate; and a second structure disposed on the semiconductor substrate and adjacent to the first structure, wherein the second structure has a second height from the upper surface of the semiconductor substrate, and the second height is substantially greater than the first height, the second structure comprises: a limiting layer disposed on the upper surface of the semiconductor substrate, wherein the limiting layer has a third height from the upper surface of the semiconductor substrate; a first polysilicon layer disposed conformally on the limiting layer and the semiconductor substrate, wherein the first polysilicon layer has a fourth height from the upper surface of the semiconductor substrate, and the third height is substantially equal to or greater than one fifth of the fourth height; and a second polysilicon layer disposed conformally on the first polysilicon layer, wherein a ridge of the second polysilicon layer is defined as a limiting block vertically aligned with the limiting layer, and is disposed near an edge of the second structure beside the first structure; an ARD layer covering the first structure, the second structure and the limiting block conform ally; a passivation layer covering the ARD layer, wherein the passivation layer comprises silicon oxynitride (SiON); a BARC layer covering the passivation layer, wherein the BARC layer comprises a low-viscosity material, and the BARC layer above a top surface of the second structure has an external surface substantially parallel to the top surface of the second structure; and a plurality of control gates disposed on the external surface of the BARC layer.
 16. The semiconductor device of claim 15, wherein the first structure includes a low gate polysilicon layer.
 17. The semiconductor device of claim 16, wherein the first polysilicon layer includes a floating gate polysilicon layer, the second polysilicon layer includes a high-voltage polysilicon layer having a first portion and a second portion, and the first portion is disposed on the first polysilicon layer.
 18. The semiconductor device of claim 17, wherein the second portion is extended along the upper surface of the semiconductor substrate and connected to the low gate polysilicon layer.
 19. The semiconductor device of claim 17, wherein the first structure includes the low gate polysilicon layer and the second portion of the high-voltage polysilicon layer disposed on the semiconductor substrate.
 20. The semiconductor device of claim 15, wherein the third height is substantially equal to or greater than one fourth of the fourth height. 